In most government fleets, diesel-powered trucks and equipment are the workhorse units. Unfortunately, the exhaust is proven harmful to the health of the very citizens we serve. According to the California Air Resources Board (CARB) and the American Lung Association (ALA), particulate matter from diesel emissions causes 15,000 premature deaths every year in the U.S.

The U.S. Environmental Protection Agency (EPA) has mandated sweeping changes to reduce these harmful emissions. Round one came in model-year 2002, round two is upon us for MY-2007, and round three is not far off in MY-2010. To complement and enable the new diesel emissions technology, the fuel’s formulation has undergone the change to low-sulfur diesel (LSD) and now, ultra low-sulfur diesel (ULSD).

Still, the very durable nature of diesel engines will result in older, dirtier technology remaining in use for more than a decade. To mitigate the negative health effects of this older technology, we can employ emissions-retrofits that are easy to implement, reliable, and even affordable — especially considering the cost in human suffering of doing nothing. The EPA estimates that a $100 million voluntary diesel retrofit program would create $2 billion in health benefits from reduced premature deaths, hospital visits, and other costs associated with diesel emissions exposure.

The Science Behind the Technology
Several emissions-reduction technologies have been EPA-certified. Two common systems are crankcase emission control systems and the diesel oxidation catalyst, which replaces the muffler. Both were explored for implementation in the city of St. Louis, Mo., fleet. However, only the catalytic mufflers were ultimately implemented.

Diesel oxidation catalyst (DOC) reduces emissions by chemically converting harmful diesel exhaust pollutants to water and carbon dioxide (CO2). The Donaldson Filtration Systems ( catalytic mufflers selected for the St. Louis project were available to fit MY-2000 Crane Carrier Corp. refuse trucks with Cummins 8.3L, 250 hp engines with vertical exhaust. They were also available to fit MY-2000 and 2001 International heavyduty dump and roll-off container trucks with various engines and horizontal exhaust. However, several other makes and models could not be retrofitted with existing hardware designs because the catalytic mufflers would not fit into the unobstructed space where the existing muffler would be removed, even with hanger, coupler, and pipe modification.

This hardware has proven to almost always perform without problems for up to several hundred-thousand miles or more.

Crankcase emission control technology can be retrofitted to control emissions from turbocharged diesel engines. One method collects and coalesces the particulate matter (PM) emissions vented from the crankcase with a filter system. This system includes filter housing, pressure regulator, pressure-relief valve, and oil check valve. The technology can be used on both on- and off-road diesel engines. However, unlike catalytic mufflers, these crankcase systems require monitoring and filter changes as part of preventive maintenance services.

Unfortunately, using this technology on the city’s refuse trucks proved impossible without hanging hardware well below the frame where it would be prone to damage and potentially damaging to the engine. Funds designated for the crankcase systems were used instead, with EPA permission, to purchase additional catalytic mufflers.

The Promise of Cleaner Emissions
Replacing a diesel vehicle’s standard muffler with a diesel oxidation catalyst device reduces engine-out unburned hydrocarbons (HC) and carbon monoxide (CO) by up to 90 percent or more, and exhaust PM by 20-50 percent, depending on exhaust temperature, fuel sulfur level, composition of engine-out PM, and other factors.

Catalytic mufflers control the particulate soluble organic fraction (SOF)by up to 90 percent. The more lubricating oil burned, the higher the exhaust particulate SOF content, so improvements in older engines are typically more dramatic than in newer ones.

These retrofit devices also reduce smoke emissions from older vehicles by more than 50 percent and virtually eliminate the pungent odor associated with diesel engines. Performance is not reduced significantly when used with conventional low-sulfur diesel fuel (up to 300-500 ppm).However, the emission control performance is enhanced when operated with ultra-low sulfur diesel fuel (ULSD) with a maximum sulfur content of 15 ppm.

Notably though, studies of real-world use showed catalytic mufflers had no impact on nitrogen oxide (NOx) emissions. NOx is a major component of the chemical soup in urban atmospheres that cooks into ozone (smog) in the presence of sunlight.

The planned-for crankcase emissions control systems that could not be installed in the St. Louis refuse fleet were proven to eliminate virtually all harmful emissions from the crankcase. This source can account for 10-25 percent of total engine emissions.

Grant Money from Partnership Helps Push Project Further
It took a partnership of the EPA, ALA of Missouri, the St. Louis Community Air Project, and the city of St. Louis Equipment Services Division to clean up the exhaust of mid-life refuse and dump trucks operating daily in city neighborhoods. In true “Show-Me-State” Missouri tradition, St. Louis has tested compressed natural gas (CNG), biodiesel (B-20), ethanol (E-85), and hybrid-electric vehicles in search of an economically viable solution to reduce harmful emissions and petroleum consumption. The opportunity to implement and demonstrate diesel emissions-reduction technology was welcomed when presented by ALA.

The EPA provided $125,000 in grant funding under its Diesel Retrofit Program. ALA provided grant administration and acquired the expert consulting services of Emissions Advantage, LLC ( The city installed the Donaldson hardware provided by the grant on 40 refuse trucks and 20 dump/roll-off container trucks. The catalytic mufflers and mounting hardware averaged about $810 per vehicle. Price is, of course, impacted by the number of units ordered and the application. The cost range is typically $500-$1,750 each.

Be advised the grant proces was not quick. Acquiring hardware for additional fleet segments and installing it should be possible in six months or less. Limited availability of precious metals for manufacturing catalytic mufflers appears to cause most of the delay.

Key milestones in St. Louis’ grant application program were:

  • July 2004 – application for federal assistance submitted.
  • February 2005 – award announced.
  • September-November 2005 – installation on refuse trucks.
  • March 2006 – “before” opacity test conducted on control refuse trucks.
  • June 2006 – “after” opacity test conducted.
  • September-November 2006 – installation on dump/roll-off trucks.

    The Results Are Self Evident
    Installing catalytic mufflers required 60-70 minutes per truck, including removing mufflers, modifying pipes and hangers, and installing reducers where necessary. The process became routine after the first few installations and required no special tools or training for experienced fleet maintenance technicians.

    No drop-off in engine power or fuel-economy occurred. However, a noticeable reduction in exhaust soot and odor did occur after a month-long new-equipment burn-in period.

    Emissions retrofit manufacturers test their products to obtain EPA and CARB approval. Unfortunately, equipment available to the state of Missouri for the St.Louis projects only allowed testing the exhaust opacity (visible smoke) of the city’s test vehicles. As indicated in Table 1, the average opacity of the two refuse trucks tested dropped more than 92 percent from a pre-retrofit average of 9.7 to a post-retrofit and three-month burn-in period of 0.7.Note that the readings immediately after retrofit were either unchanged or slightly worse. Other fleet tests showed these significant improvements occur with less than a month’s normal use.

    The Challenge in Production
    Given how effective and affordable voluntary diesel retrofit programs are, as proven in real-world fleet operations, every fleet should install emissions reduction technology on pre-MY-2002 trucks they plan to operate for several more years. Since not every diesel vehicle is a good retrofit candidate, it is even more important to retrofit those good candidates to promote positive air quality changes quickly.

    If this account and others like it haven’t been enough to convince you that investing in voluntary diesel exhaust retrofits is a good idea, consider it from the angle of selfpreservation. Most fleet personnel are subject to chronic diesel exhaust exposure for most of their adult lives. One of those 15,000 lives per year you prevent from being shortened may just be your own.

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